Field of the Invention and Related Art Statement
The present invention generally relates to an endoscope apparatus for inspecting an inside of cavities of human bodies and pipes and others of mechanical constructions.
Heretofore, there have been proposed various kinds of endoscope apparatuses. Usually, the endoscope apparatus comprises an insertion section insertable into a cavity of a human body, a light guide for transmitting illumination light from a proximal end to a distal end of the insertion section, an objective lens system arranged at the distal end of the insertion section for forming an optical image of an illuminated object under inspection, and an image guide for transmitting the optical image from the distal end to the proximal end of the insertion section. The optical image transmitted through the image guide may be inspected with the naked eye by means of an eyepiece lens system or may be picked up by a television camera to derive an image signal which is supplied to a monitor to display the image of the object. In such an endoscope apparatus, the image guide is formed by a bundle of a number of optical fibers each of which is composed of a core and a clad applied around the core. Since the clad does not serve to transmit the light therethrough, the resolution of the fiber bundle is relatively low. Particularly, in the endoscope, since the insertion section should have the small diameter, the number of fibers of the image guide is limited and thus the resolution could not be made sufficiently high. Moreover, between adjacent fibers there is a binding layer which could not transmit the light, in the optical image transmitted through the image guide there appears a dark or black network-like mesh. This dark mesh is annoying particularly when the image is enlarged.
Further, in case of using the television camera having a solid state image sensor such as charge coupled device (CCD), photodiode image sensor, MOSFET image sensor and static induction transistor (SIT) image sensor, the resolution becomes further reduced, because the resolution of the solid state image sensor itself is low. Moreover, the solid state image sensor might produce undesired Moire fringes. There is further proposed a video endoscope apparatus in which a very small solid state image sensor is arranged in the distal end of the insertion section. In this video endoscope apparatus, there might be produced the Moire fringes when the object includes stripe patterns.
In order to avoid the above mentioned black network-like mesh, in U.S. Pat. No. 3,217,589, there is proposed an endoscope apparatus in which both ends of the image guide are supported rotatably and the image guide is rotated as a whole. However, in the endoscope for medical use, the insertion section has a small diameter, so that it is practically very difficult to arrange a driving mechanism for rotating the distal end of the image guide within the insertion section.
In U.S. Pat. No. 4,141,624, there is described an endoscope apparatus in which plane parallel plates are arranged between the objective lens system and the distal end of the image guide and between the proximal end of the image guide and the eyepiece lens system, respectively and these plane parallel plates are vibrated in the same direction viewed on the image in synchronism with each other. Mechanisms for vibrating the plates are formed by electromagnetic vibrating devices. In case of using the electromagnetic device, the diameter of the distal end portion of insertion section is liable to be large.
In German Gebranchsmuster Publication No. 7,315,025, there is further proposed an endoscope apparatus in which both ends of the image guide are vibrated by means of ultrasonic transducers arranged on respective ends of the image guide. However, in order to vibrate the image guide having a relatively large weight, it is necessary apply very large ultrasonic energy to the image guide so that the dimension of the ultrasonic vibrator becomes quite large, and thus the diameter of the insertion section might be large. Moreover, the ultrasonic vibration causes another problem of heat generation and the glass fibers composing the image guide might be broken by the high frequency ultrasonic energy.
In Japanese Patent Publication Kokai No. 58-168,015, there is described an endoscope apparatus in which piezo-electric vibrating elements are provided between the both ends of the image guide and supporting members so that the ends of the image guide are vibrated in a direction perpendicular to an optical axis of the image guide. The piezo-electric element is formed by a laminated piezo-electric element. In order to vibrate the image guide end by a sufficient amount, the laminated piezo-electric element has to be long, so that the insertion section is liable to have a long diameter.
In U.S. Pat. No. 4,618,884, there is disclosed still another endoscope apparatus in which the plane parallel plates are arranged in both ends of the insertion section like as the endoscope apparatus described in the above mentioned U.S. Pat. No. 4,141,624 and are tilted by means of piezo-electric elements. However, in this endoscope apparatus, the plane parallel plates could not be swung by a sufficiently large amount for effectively removing the black mesh, because the piezo-electric element is formed by a thickness vibration type element in order to swing the plate about a center axis extending perpendicularly to the optical axis of the image guide.
It should be noted that the above mentioned prior art publications do not teach how to remove the Moire fringes which are generated in the video endoscope apparatus comprising the solid state image sensor arranged in the distal end of the insertion section. It has been proposed to arrange filters such as spacial frequency filter and double refraction filter between the objective lens system and the solid state image sensor. However, this solution is expensive and further the dimension of the apparatus becomes complicated and large.